1. Field of the Invention
The present invention relates to a coherent optical receiving apparatus and an optical signal processing method, and more particularly, to a coherent optical receiving apparatus and an optical signal processing method that accurately estimates a frequency offset to compensate for a phase distortion of the optical signal.
2. Description of the Related Art
A return-to-zero (RZ) pulse carver may be included in a transmitting apparatus to be used for optical transmission. The RZ pulse carver may be configured using a Mach-Zehnder (MZ) optical modulator, to convert a waveform to a RZ pulse. When an intensity of a provided sine-wave is the same as a voltage required by the RZ pulse carver, the RZ pulse carver may be an ideal RZ pulse carver. The provided sine-wave may be accurately divided into ½ sine-waves and provided to an internal electrode of the MZ optical modulator. In this example, phases of the provided ½ sine-waves may be the same. An intensity of the provide ½ sine-waves may be the same as the voltage required by the RZ pulse carver.
However, an actually used RZ pulse carver is different from an ideal RZ pulse carver. Therefore, a phase distortion may occur in an optical pulse generated by the RZ pulse carver. The phase distortion may deteriorate a performance of a phase-modulated signal. The phase distortion may cause an error in estimating a frequency offset that is a difference in frequency between a laser used by a transmitting apparatus and a laser used by a receiving apparatus.